Weight and Density

July 1, 2006

Roger Perrone, perrone@caer.uky.edu

University of Kentucky,

Center for Applied Energy Research

2540 Research Park Dr., Lexington, KY 40511

859-257-0227

4th grade demonstration and experiment

Overview

• Experiment Objectives

• Materials

• Experimental Steps

• General Observations and Helpful Hints

Experiment Objective

To learn about the relationship between weight and density.

To learn how relative density affects fluid flow.

To relate this to real phenomena such as weather and oceanic circulation.

Materials NeededFor Demonstration:Large bag of Styrofoam peanutsSmall bag of sand (same weight as above)Yard stick2 identical large coffee cans, each filled with either

Styrofoam peanuts or sandCarboy of water thickened with sugar and non-iodized salt

and tinted with food coloringWorld map

Per Group:Disposable vacuum filterSharp pencilCafeteria tray2 plastic beakers

Demonstration Procedure1. Prepare the bags of styrofoam and sand beforehand by

tying each one closed with equal lengths of cord ending in a loop.

2. Present the two bags, pointing out that one is much larger than the other and asking the students to guess which one is heavier.

3. Show that the bags are the same weight by sliding the loop of each cord onto the ends of a rigid yardstick and balancing the yardstick at the center. Do this on the edge of your finger so you can fudge a little if needed.

4. Have a student come to the front of the class and ask him/her to lift the coffee can filled with Styrofoam and then one filled with sand.

5. The lesson is that two objects of different size (volume) can have the same weight and two objects of the same size can have different weights. Density is the relationship between size and weight.

Experimental ProcedureHave the students do all of the following on a cafeteria tray to

simplify cleanup.• Each group should have a beaker of water and a beaker

of water/sugar/salt/food coloring, a pencil and a vacuum filter

• Separate the vacuum filter into the funnel and bottle and fill the bottle with water to the top and slightly beyond

• Carefully reassemble the vacuum filter and fill the funnel portion to about 1/3 with the colored solution

• Pierce the filter dividing the two portions with the pencil and observe the colored fluid flowing into the fluid in the lower portion. It should form a distinct colored layer on the bottom.

• Clear water will also flow into the filter portion but, this is difficult to see – give the students a few minutes to see if anyone gets it before letting them know what to look for.

Additional Demonstrations

Point out the relationship between air temperature and air density. Draw a profile of a sea coast and show how the sun warming the land more quickly than the ocean creates off-shore breezes.

On a map show how the difference in temperature between northern and tropical regions drives the winds and that all weather is a result of fluids of different density flowing over one another.

On a map show the Atlantic Conveyor, which is the circulation system for all the oceans of Earth and is also driven by differences in density.

Resources

• Ward's Scientific (www.wardsci.com)